Feeling flabby as you sit at your desk? That’s the exact problem this set of exercises was designed to prevent. We’ve mentioned it before—the 5BX workout developed for the Royal Canadian Air Force. But today we are happy to bring you these famous exercises in the form of a video (er, film reel).

The routine enjoyed popularity for decades after this film and its accompanying booklet were made. Ruth Bader Ginsburg used to do it before starting her better known exercise routines, and Kate Middleton’s friend told a tabloid in 2012 that the duchess does it too. Be sure to catch the demonstrations at 9:15 of exercises that are difficult to figure out from the written instructions.

Before you hop out of your chair to do these exercises, it’s fair to warn you that the straight leg sit-ups in “Exercise 2” have fallen out of fashion because they compress the spine; crunches and planks are the modern equivalent. The Royal Canadian Air Force stopped using these exercises—Wikipedia says in 2008 but I can’t confirm—so proceed at your own risk.